A cosmic UV/X-ray background model update

Claude André Faucher-Giguère*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

We present an updated model of the cosmic ionizing background from the UV to the X-rays. Relative to our previous model, the new model provides a better match to a large number of up-to-date empirical constraints, including: (1) new galaxy and AGN luminosity functions; (2) stellar spectra including binary stars; (3) obscured and unobscured AGN; (4) a measurement of the non-ionizing UV background; (5) measurements of the intergalactic H I and He II photoionization rates at z ∼ 0−6; (6) the local X-ray background; and (7) improved measurements of the intergalactic opacity. In this model, AGN dominate the H I ionizing background at z ≾ 3 and star-forming galaxies dominate it at higher redshifts. Combined with the steeply declining AGN luminosity function beyond z ∼ 2, the slow evolution of the H I ionization rate inferred from the high-redshift HI Ly α forest requires an escape fraction from star-forming galaxies that increases with redshift (a population-averaged escape fraction of ≈ 1 per cent suffices to ionize the intergalactic medium at z = 3 when including the contribution from AGN). We provide effective photoionization and photoheating rates calibrated to match the Planck 2018 reionization optical depth and recent constraints from the He II Ly α forest in hydrodynamic simulations.

Original languageEnglish (US)
Pages (from-to)1614-1632
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Volume493
Issue number2
DOIs
StatePublished - 2021

Keywords

  • Cosmology: theory
  • Diffuse radiation
  • Galaxies: active
  • Galaxies: formation
  • Intergalactic medium

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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